Method for the production of fiber composites and fiber composite produced according to said method

ABSTRACT

The invention relates to a method for the production of fiber composites and a fiber composite which is produced according to the method of the invention.

The invention relates to a method for the production of fibercomposites. In addition, the invention relates to a fiber compositeproduced according to the method according to the invention.

It is known to produce composites by spraying endless strands,preferably glass-fiber strands, together with hardenable, thermosettingresins onto a substrate and letting the whole thing harden. To this end,glass-fiber strands are used mainly, which are taken out of a bundle ofhundreds of elementary fibers and cut to predefined lengths, for exampleof 1 to 10 cm, by means of a cutter and at the same time are wet with aresin matrix at a certain weight ratio, for example 30% glass fibers and70% resin. These glass fiber strands are very thin, namely a few tenthsof a millimeter, and can be laid in a flat, two-dimensional randomlayer, due to their ratios of length and thickness.

Voluminized fibers within the sense of the invention are known from DE10114708 A1, as well as from EP 0 222 399 B1.

The invention is based on the object of producing three-dimensionalfiber composites having a particularly large volume and which, ifrequired, contain openings and/or cavities that can be permeable to airand liquids.

According to the invention, this object is achieved with a method havingthe features of claim 1. Advantageous embodiments and developments ofthis method are the subject matter of the subclaims referring to claim1.

Furthermore, the above-mentioned object is achieved with a fibercomposite having the features of claim 10. Advantageous embodiments anddevelopments of this fiber composite are the subject matter of thesubclaims referring to claim 10.

According to the invention, a staple fiber mat, for example, can beproduced which contains glass strands that preferably have been modifiedto voluminize the mat formed of strands by means of expandablethermoplastic hollow microspheres. This voluminization or increase ofvolume takes place by embedding non-expanded thermoplasticmicroparticles such as hollow microspheres, which contain a certainamount of inflating gas, for example butane, in the interstices betweenthe elementary fibers and then expanding them by means of a thermalprocess.

In this expansion process, the elementary fibers of the bundle of fibersare forced apart from one another, whereby the diameter and the volumeof the fiber bundle and/or of the formation consisting of staple fibersincreases by at least ten times to a hundred times. The fiber strands orother formations thus voluminized can be processed by means of anapparatus that is also suitable for the production of sprayed fiberlaminates.

During the cutting of such fiber bundles, beam-like crude fiber stablesare the result which, in contrast to the thin, non-voluminized fibers,align themselves not in two but rather in three dimensions and whichform a voluminous mat with a very open, air-permeable structure. Bymeans of suitable binding agents that are necessary anyway for fixingthe microparticles, for example microspheres, it is furthermore possibleto give the fiber composites a certain stiffness which supports themaintenance of the open structure until the resin material has hardened.

By adjusting the spraying nozzle, the amount of synthetic resin used inthe spraying process can be set so that it is just sufficient to fillthe open-pore and absorbent formations of staple fibers with resin tosaturation, while cavities still remaining between the individual staplefibers stay open. This results in the additional effect that the hollowmicrospheres embedded between the staple fibers reduce the resin uptake(in relation to the volume) by up to 50% to 60%, compared tonon-volumized fiber formations. Apart from saving weight in aconsiderable extent, it is possible to save costs in an equallyconsiderable amount.

The resin fiber spraying method may have been known for 40 years and isused, in particular, to produce a glass-fiber reinforced plasticlaminate. Surprisingly, it was established that this known sprayingmethod can also be applied to voluminized fibers. The person skilled inthe art did not expect that the comparably very light fibers can bethrown across the required distances of typically 0.5 to 2 meters inorder to reach the target, i.e. a female mold. The person skilled in theart would have expected that a female mold having a size of typically 30to 40 cm would largely be missed due to the lightness of the voluminizedfibers, and that thus, the waste would becom too large. Furthermore, alumping of the voluminized fibers hitting the female mold was to beexpected.

Instead, the very light and soft material, i.e. the voluminized fibers,do not mat together. Surprisingly, the cutting device (cutter) used tochop endless threads and/or fiber bundles is not clogged, whichotherwise would have led to a great maintenance effort.

In the processing of glass fibers known from the state of the art,static charging constitutes a big problem. Therefore, countermeasuressuch as grounding and ventilation must be taken in the processing ofglass fibers. Therefore, the person skilled in the art would haveexpected that problems relating to static charging would be all thebigger in the processing of voluminized fibers according to theinvention which consist of plastics. Surprisingly, however, this was notthe case.

These above-mentioned problems feared by the skilled person could beavoided, in particular, by sufficient wetting of the voluminized fiberswith resin particles. In this case, the kinetics are not determined bythe voluminized fibers but rather by the significantly heavier resin.The uniform distribution of the sprayed voluminized fibers on the femalemolds could thus be realized. A distance of 2 meters could be bridgedwithout problem during spraying. Small female molds were also hit withsufficient accuracy so that overly large amounts of waste and pollutionconnected therewith could be avoided.

By generating pressure in a press or by means of hand rollers, forexample, a three-dimensional mat produced in this way or the like can becompressed, at least in places, to so that a homogeneous laminate thatis free of air bubbles results in which the originallythree-dimensionally arranged staple fibers have aligned in atwo-dimensional random layer. If, however, the material is left toharden without the application of pressure after spraying on the fibermat, a three-dimensional mat with an open structure will be the result.

Depending on contructional requirements, the processing person can varyat will the density of this structure by application of more or lesspressure. It is also possible to produce areas with a flat, homogeneousstructure and areas with a very voluminous structure by means oflocalized pressure within a molded article or formation produced in thismanner. The material thicknesses can vary up to threefold between athree-dimensional mat hardened without pressure and a compressed mat.

Particularly interesting is the possibility of the production ofsandwich structures wherein a first base cover layer is produced from ahomogeneous ply of glass fibers lying flat, onto which a core ply of athree-dimensional random layer of voluminzed staple fibers is laid. Thefinal cover layer in turn is a smooth layer of two-dimensionally alignedstaple fibers.

This technology can be applied in one working step, the wet-in-wetproduction resulting in a total homogeneity of the sandwich structurethat cannot be achieved with the production method of usual sandwichstructures, by embedding light but foreign materials, for example woodor foamed plastic. The entire sandwich structure then consists of cutstaple fibers that hook into each other at the boundary surfaces. Coverlayers that can consist of glass fiber material are therefore not bondedwith the core material. Thus, a novel product with superior technicalproperties results. In comparison to the sandwich structures in whichcover layers were bonded with a middle ply, it was possible to improvethe shear strength, the flexural rigidity as well as the elastic modulusat the same material thicknesses and weights of cover layers and corematerial. Increases in the above mentioned technical parameters by 20%to 30% were effected.

The costs of production were also significantly lowered, because onegluing step can be omitted and cover plies and core material areproduced in one working step. Glass fibers, for example, are thereforesprayed for the production of cover plies. The core material isgenerated by spraying the voluminised fibers.

Sandwich structures produced in an open system in this manner have aextremely low specific weight and are of the highest dimensionalstability, in particular with respect to flexural rigidity and shearingstrength.

According to the invention, fenders for an automobile, bumpers,spoilers, air deflectors, motor covers for electric motors, deck hatchesfor a boat, floor tiles, panels, children's toys such as slides as wellas gardening tools are produced in particular. These are typical smallparts or small molds.

EXAMPLE

Strands of glass fibers that have been voluminized by embeddingthermoplastic hollow microbodies are sprayed onto a female mold by meansof a resin-fiber-spraying gun. Here, the endless strands aresimultaneously chopped into staple fibers of, for example, 3 cm lengthby means of a cutter and sprayed onto the female mold together with adirected spray of hardenable resin such as unsaturated polyester. Theamount of resin used is set so that it is just sufficient for thesaturation of the absorbent staple fibers. The proportion of resinamounts to about 50% in relation to the fiber volume.

The expanded staple fibers have a beam-like and voluminous structure sothat a mat layer thus resulting aligns in a three-dimensionalarrangement of the stable fibers. The synthetic resin sprayed outsimultaneously is absorbed by the porous staple fibers, with cavitieslocated between the staple fibers remaining open and air-permeable.After the resin has hardened, the result is a composite of extremelyhard staple fibers aligned three-dimensionally which yield a compositematerial which is both light and has great static strength that iscomparable at the contact and crossing points with so-called chevaux defrise.

A composite produced in this manner can also be used as a core layer ofa sandwich structure by covering this composite with two external coverplies of non-voluminized thin fiber composites. In these cover layers,the necessary amount of resin in relation to the fiber volume is about95%. The thicknesses of the individual layers depend on the desiredconstructional requirements.

Due to the production of the sandwich structure which is possible in oneworking step (wet-in-wet), mechanical strengths can be achieved inrelation to the specific weight that can be achieved with almost noother sandwich structure.

Areas of use for such composites are given wherever greatest strengthsat the lowest possible weight are desirable, for example, in theproduction of boats, vehicles, airplanes, fan blades, containers,formwork panels and the like.

For the purpose of further illustration of the invention, an embodimentof the mat-shaped composite is represented schematically in the drawing,wherein

FIG. 1 shows a top view onto a section of the mat-shaped composite

FIG. 2 shows a cross-section of the composite of FIG. 1.

It can be seen from the top view of a mat-shaped composite (1) shown inFIG. 1 that it contains randomly laid staple fibers (2) which areembedded in a matrix (3) of hardenable thermosetting synthetic resin andare thus held together. Between the staple fibers (2), thermoplastichollow microspheres are embedded which cannot be seen in the drawingthat have been expanded under the influence of heat so that the matrix(3) with the staple fibers (2) embedded therein in the form of a randomlayer form a three-dimensional composite.

The composite (1) is formed in the shape of a sandwich, as FIG. 2 shows.On a three-dimensional core layer (4), a top cover ply (5) and a bottomcover ply (6) are disposed. In contrast to the core layer (4), the coverplies (5) and (6) are formed two-dimensionally, so to speak, since noexpandable thermoplastic hollow microspheres or similar microbodies areembedded between the staple fibers of these layers.

FIG. 2 reveals that cavities (7) are contained in the matrix (3) of thecore layer (4) that make the mat-shaped composite (1) permeable to airand liquids.

In contrast to the core layer (4), the cover plies (5) and (6) are freeof bubbles and therefore formed leakproof, as can be seen from FIG. 2.

By the invention, the production of sandwich molded articles ofcomposite materials that are not produced in the closed system, i.e. bypressing in a mold consisting of two mold halves, but rather in theso-called open system.

1-18. (canceled)
 19. Method for the production of fiber composites,wherein staple fibers that are soaked with hardenable thermosettingsynthetic resin and cut to length are laid in a three-dimensional randomlayer and thus are bound together.
 20. Method according to claim 19,wherein the staple fibers have a length of 0.5 to 20 cm.
 21. Methodaccording to claim 19, wherein the staple fibers comprise glass fibers.22. Method according to claim 19, wherein the staple fibers compriseplastic.
 23. Method according to claim 19, wherein the staple fiberscomprise carbon fibers.
 24. Method according to claim 19, wherein beforeor during the laying of the staple fibers, said staple fibers havehollow thermoplastic microspheres embedded therebetween.
 25. Methodaccording to claim 24 wherein the hollow thermoplastic microspherescontain an inflating gas, and wherein the hollow thermoplasticmicrospheres are expanded by heating the inflating gas.
 26. Methodaccording to claim 19, wherein the cut staple fibers are wetted with ahardenable synthetic resin selected from the group consisting ofunsaturated polyester, epoxy resin, polyurethane resin, vinyl esterresin and phenolic resin in an amount sufficient to saturate the staplefibers, wherein cavities between the three-dimensionally arranged staplefibers remain open.
 27. Method according to claim 19, wherein thethree-dimensional random layer is provided on at least one side with asmooth, homogeneous, two-dimensional layer of non-volumized fibers. 28.Method according to claim 19, wherein the three-dimensional random layeris at least partially compressed to a homogeneous composite layer thatis free of bubbles.
 29. Fiber composite consisting of a matrix ofhardened thermoplastic synthetic resin and staple fibers embeddedtherebetween in a random three-dimensional arrangement.
 30. Fibercomposite according to claim 29, wherein the matrix includes cavitiesthat are gas-permeable liquid-permeable or both.
 31. Fiber compositeaccording to claim 29, wherein the matrix contains cut staple fibershaving a length of 0.5 to 20 cm.
 32. Fiber composite according to claim31, wherein the staple fibers are selected from the group consisting ofglass fibers and carbon fibers.
 33. Fiber composite according to claim29, wherein the cut staple fibers are volumized by embedding hollowthermoplastic microspheres therebetween.
 34. Method according to claim33 wherein the hollow thermoplastic microspheres contain an inflatinggas and wherein the hollow thermoplastic microspheres are expanded byheating the inflating gas.
 35. Fiber composite according to claim 29,wherein the three-dimensionally arranged staple fibers are wetted with ahardenable synthetic resin selected from the group consisting ofunsaturated polyester, epoxy resin, polyurethane resin, vinyl esterresin, and phenolic resin, in an amount sufficient to saturate theabsorbent staple fiber bundles, wherein cavities between thethree-dimensionally arranged staple fibers remain open.
 36. Fibercomposite according to claim 29, wherein the cut staple fibers arearranged in the shape of a sandwich structure, wherein a core layerresides between a first cover layer and a second cover layer, whereinthe core comprises a three-dimensionally arranged random layer ofvolumized staple fibers and the first and second cover layers eachcomprise a smooth, homogeneous, two-dimensionally arranged layer ofnon-volumized fibers.
 38. Fiber composite according to claim 29, whereina portion of the cut staple fibers, are compressed to a homogeneouscomposite layer free of air bubbles, and a portion of the cut staplefibers, not processed with pressure, remain randomly arranged in athree-dimensional random layer.
 39. Construction component comprising afiber composite according to claim 29, wherein the constructioncomponent is selected from the group consisting of a fender, a bumper, aspoiler, an air deflector, a motor cover for electric motors, a deckhatch, a flap gate, a floor tile, a panel, or a children's toy.